Pyroclastic flow hazard at Arenal volcano, Costa Rica: scenarios and assessment

The present work provides a comprehensive understanding of the evolution of pyroclastic flow hazard at Arenal volcano, Costa Rica, during the recent period of volcanic activity. It uses the geophysical flow model TITAN2D to analyze and summarize pyroclastic flow hazard patterns associated with the topographic development of the volcanic edifice (“radial hazard pattern”) and to an observed evolution in the nature of pyroclastic flows at Arenal (“concentric hazard pattern”). In this regard, a new classification of pyroclastic flows of gravitational origin at Arenal is proposed and characterized, presenting different levels of associated hazardousness. TITAN2D has been used as a basis to produce pyroclastic flow hazard maps for two defined scenarios: a “current” hazard scenario, considered as being fairly representative of the present-day situation at Arenal; and another scenario which is thought could represent a stage in future pyroclastic flow hazard where crater C has largely engulfed crater D as a result of topographic change. These two maps show significantly different hazard distributions, and demonstrate the need for frequent updates of hazard assessments in this and other similarly dynamic volcanic settings. In the case of Arenal, this implies a need for regularly updating the topographic models of the volcano to capture topographic changes that impact the distribution of volcanic flow hazard. Furthermore, this work provides a detailed evaluation of TITAN2D regarding its suitability to form the basis of such hazard assessments.